Paper Density

Paper density (also known as basis weight and grammage) is a term used in the pulp and paper industry and also for fabric industry to denote a measure of mass of the product per unit of area for a type of fabric, paper or paperboard. The term "density" is not used in its traditional sense of mass per unit volume. "Paper density", rather, is a measure of the area density. Paper products that let little or no light pass through (e.g. poster board) are considered dense or heavy. Paper products that allow some light to pass through (e.g. tissue paper) are considered lightweight. In the pulp and paper industry, it is common to set a commercial paper machine to produce paper to a target paper density. Paper density can also be used to distinguish paper from paperboard as the latter usually has a grammage greater than 134 g/m².

Two ways of expressing paper density are commonly used:

• Expressed in grams per square meter (g/m²), paper density is also known as grammage. This is the measure used in most parts of the world.
• Expressed in terms of the mass (expressed as weight) per number of sheets, it is known as basis weight. The convention used in the United States and a few other countries using US paper sizes is pounds of a ream of 500 (or in some cases 1000) sheets of a given (raw, still uncut) basis size. Japanese paper is expressed as the weight in kg of 1000 sheets.